RexWeather User Guide

RexWeather is built for tornado enthusiasts who want the full picture: current weather, active severe weather signals, official SPC outlooks, a transparent Tornado Potential score, and historical tornado records from 1950 to the present. This guide walks through the app from first launch to deeper historical exploration.

Getting Started Locations Live Alerts SPC Outlooks Tornado Potential Tornado History Tornado Explorer Nearby History Settings Offline Mode Accessibility Troubleshooting

Getting Started

First Launch

Allow location access. RexWeather uses your location to show local weather, NWS alerts, SPC risk, Tornado Potential, and nearby tornado history. Precise location gives the best results.
Let weather load. Current conditions appear immediately with weather-adaptive backgrounds and night-aware condition icons.
Let tornado data finish loading. Historical NOAA tornado records download in the background on first launch. A progress indicator appears while the archive is preparing.
Pull to refresh. Swipe down on the Home screen to refresh weather, alerts, SPC data, and Tornado Potential together.

Main Weather Display

The Home screen shows temperature, feels-like temperature, humidity, wind, current condition, update time, and offline status when cached weather is being used. Animated backgrounds respond to clear, rain, snow, thunderstorm, and night conditions, while Low Power Mode and app backgrounding pause animations to conserve battery.

Choosing Your Location

RexWeather can follow your GPS location or any saved city. Tap the location name at the top of the Home screen to open the Locations sheet.

Current Location and Saved Cities

Current Location uses device GPS and shows a location arrow indicator.
City search uses MapKit geocoding with a short debounce so results update as you type.
Saved cities stay in the Saved section. Tap one to activate it, or swipe left to delete it.
Active location scope includes weather, alerts, SPC outlooks, Tornado Potential, Nearby Tornado History, and the initial Tornado Explorer center.

Live NWS Severe Weather Alerts

For US locations, RexWeather fetches active National Weather Service alerts from api.weather.gov. When alerts exist, a color-coded alert card appears on the Home screen. Tap it to read the complete alert text.

Visual Treatment	Examples	Meaning
Purple / pulsing	PDS Tornado Warning, Tornado Emergency	Highest urgency tornado wording. Follow official instructions immediately.
Red	Tornado Warning, Flash Flood Emergency, Severe Thunderstorm Warning	Immediate threat or warning-level hazard.
Amber	Tornado Watch, Severe Thunderstorm Watch, Flash Flood Watch	Conditions are favorable or significant hazards are possible.
Blue	Special Weather Statement, Wind Advisory, Dense Fog Advisory	Lower-tier advisory or statement information.

NWS alerts are US-only. For Canadian locations, RexWeather skips the NWS request instead of showing an error.

SPC Convective Outlooks

The SPC Outlook tile on the Home screen shows your current Day 1 categorical risk. Tap it to open a full-screen NOAA Storm Prediction Center outlook map.

Day Tabs and Hazard Layers

Day 1 shows today's outlook and typically updates every 1-3 hours.
Day 2 shows tomorrow's outlook.
Day 3 shows the day-after outlook.
Hazard layers include Categorical, Tornado, Wind, and Hail for Day 1 and Day 2; Day 3 includes Categorical and Probabilistic severe layers.

Reading the Map

Risk polygons use the official SPC color palette. The bottom sheet identifies the risk at your active location, shows timing metadata, and expands to reveal the layer legend plus SPC forecaster discussion text. The map remains interactive when the sheet is collapsed, so you can pan and zoom while keeping the key risk summary visible.

Risk	Meaning
TSTM	Thunderstorms possible, organized severe weather not expected.
MRGL	Marginal Risk, isolated severe storms possible.
SLGT	Slight Risk, scattered severe storms possible.
ENH	Enhanced Risk, numerous severe storms possible.
MDT	Moderate Risk, widespread severe storms likely.
HIGH	High Risk, exceptional outbreak potential.

SPC outlooks cover the continental United States. For Canada and other non-CONUS locations, the SPC tile and map are hidden while other app features continue to work.

Tornado Potential

The Tornado Potential card estimates how favorable conditions are for tornado development at your active location over roughly the next 6 hours. It displays a 1-10 score, a color-coded label from None to Extreme, a short explanation, and a safety disclaimer. It is not an official forecast and should never be used for shelter decisions.

How the Score Is Calculated

The score uses a cascade model where the strongest source wins rather than simply adding everything together.

Source	What It Checks	Why It Matters
NWS active alerts	Tornado warnings, PDS wording, tornado watches, severe thunderstorm alerts	Live official alerts take priority because the threat is already observed or imminent.
SPC tornado probability	Day 1 tornado probability polygons and categorical fallback	Official convective outlooks provide meteorologist-issued risk context.
Atmospheric ingredients	Dew point, LCL, storm signal, wind gusts, CAPE, Lifted Index, shear, CIN, convective precipitation	Ingredient scoring helps identify setups when no alert or SPC tornado polygon is present.

Model Ingredients from Open-Meteo

RexWeather uses Open-Meteo GFS model data for CAPE, Lifted Index, low-level shear, 0-6 km bulk shear, convective precipitation, dew point fallback, and CIN. These values help distinguish a truly quiet day from a loaded atmosphere where storm ingredients are present but initiation has not happened yet.

Detail Sheet

Tap the Tornado Potential card to open the Scoring Ingredients detail sheet. Chips are grouped and sorted by impact: green dot boosters, gray neutral factors, and red blockers. Each chip includes a plain-English label, a technical value when useful, and a short explanation of what that ingredient means.

Guardrails and Context

Cold-weather guardrails cap scores when the surface is too cold or too dry for meaningful tornado potential.
Geographic context recognizes Tornado Alley, Dixie Alley, the Canadian Prairies, and Southern Ontario during peak seasons.
Loaded atmosphere language appears when CAPE and shear are meaningful even if the final score remains moderate.
Canadian support skips US-only NWS and SPC services but still uses Open-Meteo ingredient data worldwide.

Historical Tornado Data

RexWeather includes over 75 years of tornado information, pairing official NOAA SPC historical records from 1950 onward with NOAA NCEI current-year tornado records. The app caches data so historical exploration remains available after the initial download.

Rating Scales

Modern tornadoes use the Enhanced Fujita Scale. Pre-2007 tornadoes use the original Fujita Scale, and RexWeather displays the correct wind speed ranges for the era.

Rating	Enhanced Fujita Wind	Original Fujita Wind	Color
0	65-85 mph	40-72 mph	Green
1	86-110 mph	73-112 mph	Blue
2	111-135 mph	113-157 mph	Yellow
3	136-165 mph	158-207 mph	Orange
4	166-200 mph	208-260 mph	Red
5	>200 mph	261-318 mph	Purple

Tornado Detail Maps

Tap a tornado anywhere in the app to open its detail view. You can review date and time, rating, path length, maximum width, start and end coordinates, nearby cities, casualties, property damage, and a map of the path.

NOAA DAT Damage Polygons

When NOAA Damage Assessment Toolkit data is available, RexWeather replaces the simple track line with surveyed damage polygons. Different path segments can be colored by their surveyed EF intensity, and a DAT enhancement badge confirms that the geometry is based on post-storm survey data. If DAT data is unavailable, RexWeather falls back to a proportional width corridor or a simple EF/F-colored path line.

Tornado Explorer

Tornado Explorer is the main research view for browsing the tornado archive on a map. It is built for quick discovery and deeper filtering.

Quick Selections

Famous outbreaks include the 2011 Super Outbreak, Moore 1999, 1974 Super Outbreak, Moore 2013, Dixie Alley 2014, and Joplin 2011.
Historical periods include the Fujita Scale Era, Doppler Revolution, Enhanced Fujita Era, Photography Era, and Storm Chasing Era.
Smart setup automatically applies date ranges, EF/F minimums, map center, and radius for the selected outbreak or era.

Filters

Open the filter sheet to adjust date ranges, quick ranges, and minimum EF/F rating. The default range is the last 15 years for smoother nationwide performance, while All Time opens the full archive. The map renders up to 500 tornadoes at once for responsiveness.

Nearby Tornado History

Nearby Tornado History searches around the active location, whether that is GPS or a saved city. The default radius is 20 miles and can be changed in Settings from 5 to 50 miles.

Map view shows tornado points, tracks, EF/F colors, and the selected search radius circle.
List view shows date, distance, rating, width, casualties, and other quick facts.
Deduplication merges multi-county segments so one physical tornado appears once.
Selected-location behavior means switching from GPS to Chicago, for example, searches around Chicago rather than your device's current position.

Settings and Customization

Tap the gear icon on the Home screen to customize RexWeather.

Appearance

Theme can follow System, stay Light, or stay Dark.
Map style can be Standard, Hybrid, Satellite/Imagery, or Muted, and applies across Explorer, Detail, and History maps.

Weather and Tornado Preferences

Temperature units switch between Fahrenheit and Celsius.
Wind speed units switch between mph and km/h.
Tornado search radius controls Nearby Tornado History and related nearby searches.

Cache Management

SPC Tornado Data covers historical records and shows cache size plus last updated time.
NCEI Current-Year Data adds recent tornado records and refreshes on a shorter cycle.
DAT Path Polygons stores surveyed damage geometry for instant repeat views.
Clear cache buttons are available if you need to free storage or force fresh data.

Offline Mode

RexWeather automatically caches successful weather and tornado data. When the network is unavailable, the app uses cached weather, keeps historical tornado tools available, and shows an offline indicator with the age of the cached data.

Best Offline Results

Open RexWeather while online before traveling or entering poor coverage.
Wait for weather and tornado data to finish loading.
Open tornado features once to make sure the archive is ready.
Check the updated timestamp so you know how fresh the cached weather is.

First-time users need an internet connection for the initial tornado archive download. If the app was deleted, reinstalled, or its data was cleared, the cache must be rebuilt online.

Accessibility

VoiceOver labels and hints are provided for cards, maps, filters, and controls.
Dynamic Type supports system text-size preferences.
Touch targets follow iOS-friendly sizing for easier interaction.
Reduce Motion and high-contrast-friendly visuals are respected where applicable.

Troubleshooting

Location Is Not Working

Open iOS Settings, then Privacy & Security, then Location Services.
Find RexWeather and allow location access while using the app.
Enable Precise Location for best local tornado and risk results.
Reopen RexWeather and pull to refresh.

Weather or Alerts Are Not Loading

Check your internet connection.
Pull to refresh on the Home screen.
Remember that NWS alerts are US-only and SPC outlooks are CONUS-only.
Force close and reopen the app if data appears stuck.

Tornado Data Is Missing

On first launch, wait for the historical tornado data loading indicator to finish.
Increase the nearby search radius in Settings.
Check Tornado Explorer filters, especially date range and minimum EF/F rating.
If offline, reconnect once so the archive can download or refresh.

Maps Feel Slow

Use the last 15 years range or a smaller geographic area when browsing nationally.
Close GPU-heavy background apps before extended map exploration.
Use Wi-Fi when loading map tiles and large tornado datasets.
Restart the device if animations or map gestures feel unusually choppy.

Safety reminder: RexWeather is an educational and situational-awareness tool. For warnings, watches, shelter decisions, and emergency action, always follow the National Weather Service and local emergency management.